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Quantifying the benefits of improved rolling of chip seals : final report

88
7. ROLLING PATTERNS
7.1 Experimental Program
One of the important variables in chip seal construction is the rolling pattern. The rolling
pattern must completely cover both edges and the center of the lane to achieve proper aggregate
embedment before the breaking of the emulsion. The rolling pattern is designed according to the
number of rollers and the type of roller used. Various rolling patterns are currently used by each
Division of the NCDOT as well as by other state DOTs. The California DOT ( Caltrans 2003)
requires a rolling pattern that uses a minimum of two rollers to cover the entire width of the lane.
The Texas DOT ( 2004) has developed the most efficient rolling system, which uses three or four
pneumatic tire rollers. Each Division of the NCDOT uses a different number of rollers and a
different type of roller. Thus, the rolling pattern is determined as a function of the number of
rollers and the type of roller. In order to determine an optimal rolling pattern in this study, a total
of five rolling patterns are designed as a function of the number of rollers and type of roller
based on current NCDOT patterns.
The rolling patterns were constructed on the same road, New Sandy Hill Church Road
( SR 1131) near Bailey in Wilson County, NC. Case I and Case II were constructed June 12, 2007.
The other three cases were constructed October 9, 2007. The application rates for the aggregate
and emulsion are 17 lb/ yd2 and 0.35 gal/ yd2, respectively. Division 4 provided an aggregate
spreader for the granite 78M and an emulsion sprayer. Division 5 provided both the combination
roller and pneumatic tire roller and division 8 was provided a combination roller.
Schematic diagrams of rolling pattern designs as a function of both number of rollers and
roller type are illustrated in Figure 7- 1. The rolling patterns shown in Figure 7- 1 ( a) and Figure
7- 1 ( b) illustrate the possible rolling patterns using two rollers. The pattern shown in Figure 7- 1
( a), Case I, is currently used by the NCDOT. Each roller applies one coverage to the entire
rolling area with three passes. The first roller follows the aggregate spreader to apply the initial
rolling before the breaking of the emulsion. The second roller begins when the first roller moves
into its third pass. The target number of coverages in this pattern is two, because it is difficult to

88
7. ROLLING PATTERNS
7.1 Experimental Program
One of the important variables in chip seal construction is the rolling pattern. The rolling
pattern must completely cover both edges and the center of the lane to achieve proper aggregate
embedment before the breaking of the emulsion. The rolling pattern is designed according to the
number of rollers and the type of roller used. Various rolling patterns are currently used by each
Division of the NCDOT as well as by other state DOTs. The California DOT ( Caltrans 2003)
requires a rolling pattern that uses a minimum of two rollers to cover the entire width of the lane.
The Texas DOT ( 2004) has developed the most efficient rolling system, which uses three or four
pneumatic tire rollers. Each Division of the NCDOT uses a different number of rollers and a
different type of roller. Thus, the rolling pattern is determined as a function of the number of
rollers and the type of roller. In order to determine an optimal rolling pattern in this study, a total
of five rolling patterns are designed as a function of the number of rollers and type of roller
based on current NCDOT patterns.
The rolling patterns were constructed on the same road, New Sandy Hill Church Road
( SR 1131) near Bailey in Wilson County, NC. Case I and Case II were constructed June 12, 2007.
The other three cases were constructed October 9, 2007. The application rates for the aggregate
and emulsion are 17 lb/ yd2 and 0.35 gal/ yd2, respectively. Division 4 provided an aggregate
spreader for the granite 78M and an emulsion sprayer. Division 5 provided both the combination
roller and pneumatic tire roller and division 8 was provided a combination roller.
Schematic diagrams of rolling pattern designs as a function of both number of rollers and
roller type are illustrated in Figure 7- 1. The rolling patterns shown in Figure 7- 1 ( a) and Figure
7- 1 ( b) illustrate the possible rolling patterns using two rollers. The pattern shown in Figure 7- 1
( a), Case I, is currently used by the NCDOT. Each roller applies one coverage to the entire
rolling area with three passes. The first roller follows the aggregate spreader to apply the initial
rolling before the breaking of the emulsion. The second roller begins when the first roller moves
into its third pass. The target number of coverages in this pattern is two, because it is difficult to